Addition polymers derived from norbornene-type monomers exhibit a number of physical and mechanical properties, some of which are highly desirable while others are less desirable or even undesirable. For example, the addition homopolymer of norbornene, i.e., poly(bicyclo[2.2.1.]hept-2-ene) exhibits some excellent characteristics such as optical clarity, low moisture absorption, and extremely high thermomechanical resistance having a glass transition temperature of about 380.degree. C. On the other hand, this same homopolymer is very brittle requiring improved toughness for many applications. A well known effective method of improving the properties of a polymer is to blend or alloy the polymer with another polymer (or polymers) in order to optimize a given property, e.g., toughness or heat distortion temperature.
A polymer blend is simply a mixture of two or more polymers. The polymer blend, however, can be either immiscible or miscible depending on the value of the free energy of mixing between the polymeric species. For a negative free energy of mixing, the thermodynamics are favorable for a miscible polymer blend; typically a one-phase system results. For a positive free energy of mixing an immiscible polymer blend results giving, typically, a multi-phase system. To change the morphology of a blend, the interfacial properties of the blend must be changed. One method to accomplish this is to add a compatibilizing agent to the blend. According to L. A. Utracki (Polymer Alloys and Blends. Thermodynamics and Rheology. Hanser, Munich, 1989, p. 124) the "goal of compatibilization is to obtain a stable and reproducible dispersion which would lead to the desired morphology and properties." This can be accomplished in the following ways: 1) add linear, graft, or random copolymers to a polymer blend; 2) coreact in the blend to generate in-situ either copolymer, interacting polymers or interpenetrating networks (by the synthesis of one of the polymers in the presence of the second polymeric constituent); or 3) modify the homopolymers by incorporation of functional groups. In many cases this may result in the formation of a polymer alloy, that is, an immiscible polymer blend having a modified interface or morphology. The morphology of the polymer alloy may be a very fine (sub-micron) dispersion or relatively large depending on the compatibilizer chosen, the amount of compatibilizer added, and the desired properties of the alloy.
Incompatibility is the rule rather than the exception, particularly in the case of hydrocarbon addition polymers derived from norbornene-type monomers (e.g., polynorbornene). Blends of incompatible polymers in most instances form large domains with properties inferior to the constituents, therefore compatibilizer techniques are usually employed to maximize the strengths of the constituents while overcoming their individual deficiencies. Various attempts have been undertaken to prepare polymer compositions that are easily processable and which possess improved physical properties. Compatibilization can provide for specific interactions between polymers. In this regard, methods have focused upon the preparation and use of functionalized polymers having pendant reactive groups which facilitate the grafting of coreactive materials and other polymers to form graft-modified polymers and polymer blends having improved physical properties. Typically a polymer can be functionalized by copolymerizing the monomer with monomer(s) having a functional substituent. However, polyolefins particularly polynorbornene-type addition polymers are generally more difficult to functionalize by copolymerization processes because of the tendency of the polar groups in the monomers to poison the catalyst. To our knowledge no attempts have been made to prepare blends and alloys of polycyclic addition polymers derived from norbornene-type monomers with a variety of other dissimilar polymers.
Accordingly, it would be highly desirable to provide blends and alloys of addition polymerized norbornene-type monomers with other polymer systems.